There have been numerous attempts in the prior art to provide flame retardant thermoplastics. Typically it has been necessary to heavily fill the plastic or thermoplastic material with additives until the desired degree of flame retardancy had been achieved. However, this offered several disadvantages insofar as a large proportion of additives could normally be expected to detract from the physical properties of the plastic base. Furthermore, it was not unusual to find in a single system large quantities of halogen-containing materials as well as metal compounds.
It will be seen that the present invention provides improved flame retardant compounds which not only improve both flame retardancy and physical properties, but also avoid the necessity for utilizing organic halides and certain metal compounds such as antimony oxide, which may be undesirable in certain applications.
In Frye, U.S. Pat. No. 4,387,176, there is disclosed flame retardant compositions comprising 50 to 97 percent by weight of thermoplastic, 1 to 40 percent by weight of a silicone base, 1 to 20 percent by weight of a metal organic compound and 1 to 20 percent by weight of a silicone resin such as MQ resin which is soluble in the silicone base.
In Ashby, U.S. Pat. No. 4,496,680, there are disclosed flame retardant nylons comprising 50-90 percent by weight nylon and 10-50 percent by weight of a flame retardant additive comprising 20 to 75 percent by weight of low molecular weight siloxanediols wherein all the organo groups bonded to silicon are phenyl, 3 to 30 percent by weight Group IIA metal C.sub.6 -C.sub.20 carboxylic acid salt, 10 to 60 percent by weight aluminum trihydrate and 10 to 50 percent by weight of an organohalide.
In Pawar, U.S. Pat. No. 4,871,795, there is disclosed silicone based flame retardants for thermoplastics which comprise (A) 100 parts by weight of a thermoplastic resin and (B) from about 2 to about 30 parts by weight of a flame retardant additive comprising (i) 20 to 60 percent by weight of a silicone oil, (ii) 10 to 40 percent by weight of a silicone resin and (iii) 5 to 60 percent by weight of a phosphorous and nitrogen containing gassing agent.
In MacLaury et al., U.S. Pat. No. 4,273,691, there is described a flame retardant composition of 70 to 98 percent by weight organic polymer, 1 to 10 percent by weight of silicone and 1 to 20 percent by weight of Group IIA metal C.sub.(6-20) carboxylic acid salt.
In Betts et al., U.S. Pat. No. 4,123,586, there is disclosed preparing flame resistant crosslinked polyolefins by adding thereto a decabromyldiphenyl ether, silicone gum and dibasic lead phthalate.
Also to be mentioned is Frye et al., U.S. Pat. No. 4,536,529, wherein the patentees teach that small amounts of magnesium hydroxide can be used with stearic acids as a reactive precursor to certain metal soaps, which are then added to certain silicone resins and silicone fluids to produce a flame retardant additive for thermoplastic resins.
Thus, it can be seen that none of the prior art disclosures teach or suggest a flame retardant additive comprising silicone treated magnesium hydroxide which is surprisingly effective in improving physical properties in addition to flame retardancy. Accordingly, the claimed compositions satisfy a long felt need in the art for a flame retardant agent which is effective at improving both the flame retardancy and physical properties of thermoplastic resins. Applicants have now found that by adding high loadings of silicone treated magnesium hydroxide to thermoplastic resins there is provided a composition which not only has improved flame resistance, but also unexpectedly has improved physical properties.